fix: improve error message from snapd pack (#5188)

Signed-off-by: Sergio Schvezov <[email protected]>
Co-authored-by: Imani Pelton <[email protected]>

docs/reference/changelog.rst

@@ -70,6 +70,15 @@ Changelog
 
   For a complete list of commits, check out the `X.Y.Z`_ release on GitHub.
 
+8.6.0 (2025-Jan-20)
+-------------------
+
+Core
+====
+
+* Improved error messaging when unable to pack.
+
+
 8.5.1 (2024-Dec-17)
 -------------------
 

requirements-devel.txt

@@ -51,7 +51,7 @@ craft-archives==2.0.1
     # via
     #   craft-application
     #   snapcraft (setup.py)
-craft-cli==2.12.0
+craft-cli==2.13.0
     # via
     #   craft-application
     #   snapcraft (setup.py)

requirements-docs.txt

@@ -65,7 +65,7 @@ craft-archives==2.0.1
     # via
     #   craft-application
     #   snapcraft (setup.py)
-craft-cli==2.12.0
+craft-cli==2.13.0
     # via
     #   craft-application
     #   snapcraft (setup.py)

requirements.txt

@@ -33,7 +33,7 @@ craft-archives==2.0.1
     # via
     #   craft-application
     #   snapcraft (setup.py)
-craft-cli==2.12.0
+craft-cli==2.13.0
     # via
     #   craft-application
     #   snapcraft (setup.py)

snapcraft/errors.py

@@ -16,6 +16,7 @@
 
 """Snapcraft error definitions."""
 
+import subprocess
 from typing import Optional
 
 from craft_cli import CraftError
@@ -180,3 +181,25 @@ class SnapcraftAssertionError(SnapcraftError):
 
     Not to be confused with Python's built-in AssertionError.
     """
+
+
+class SnapPackError(SnapcraftError):
+    """Snapd packing error."""
+
+    def _get_error_string_from_stderr(self, stderr: str | None) -> str | None:
+        if stderr is None:
+            return "snapd did not report an error"
+
+        error_lines = (err for err in stderr.splitlines() if err.startswith("error: "))
+        clean_error_lines = [err[len("error: ") :] for err in error_lines]
+        # There shall only be one
+        try:
+            return clean_error_lines[-1]
+        except IndexError:
+            return "snapd did not report an error"
+
+    def __init__(self, call_error: subprocess.CalledProcessError) -> None:
+        super().__init__(
+            message="Snapd failed to pack",
+            details=self._get_error_string_from_stderr(call_error.stderr),
+        )

snapcraft/pack.py

@@ -122,17 +122,12 @@ def _pack(
             command, capture_output=True, check=True, universal_newlines=True
         )
     except subprocess.CalledProcessError as err:
-        msg = str(err)
-        details = None
-        if err.stderr:
-            details = err.stderr.strip()
-        raise errors.SnapcraftError(msg, details=details) from err
+        raise errors.SnapPackError(err) from err
 
     return Path(str(proc.stdout).partition(":")[2].strip()).name
 
 
 def _retry_with_newer_snapd(func):
-
     @wraps(func)
     def retry_with_edge_snapd(
         directory: Path, output_dir: Path, compression: Optional[str] = None

tests/unit/test_errors.py

@@ -16,6 +16,9 @@
 
 """Snapcraft error tests."""
 
+import subprocess
+import textwrap
+
 import pytest
 
 from snapcraft import errors
@@ -40,3 +43,86 @@ def test_maintenance_base_fallback():
     assert str(error) == "'unknown-base' is not supported on this version of Snapcraft."
     assert error.resolution is None
     assert error.docs_url == "https://snapcraft.io/docs/base-snaps"
+
+
+def test_snap_pack_error():
+    error = errors.SnapPackError(
+        call_error=subprocess.CalledProcessError(
+            returncode=1,
+            cmd=["snap", "pack"],
+            stderr=textwrap.dedent(
+                """\
+                2024/12/20 11:25:37.751687 container.go:411: in snap "my-snap-name": path "this/file/does/not" does not exist
+                2024/12/20 11:25:37.751693 container.go:411: in snap "my-snap-name": path "this/file/does" does not exist
+                2024/12/20 11:25:37.751697 container.go:411: in snap "my-snap-name": path "this/file" does not exist
+                2024/12/20 11:25:37.751700 container.go:411: in snap "my-snap-name": path "this" does not exist
+                error: referenced command not found in snap
+                """
+            ),
+        )
+    )
+
+    assert str(error) == "Snapd failed to pack"
+    assert error.details == "referenced command not found in snap"
+    assert error.resolution is None
+    assert error.docs_url is None
+
+
+def test_snap_pack_error_keep_last_error():
+    error = errors.SnapPackError(
+        call_error=subprocess.CalledProcessError(
+            returncode=1,
+            cmd=["snap", "pack"],
+            stderr=textwrap.dedent(
+                """\
+                2024/12/20 11:25:37.751687 container.go:411: in snap "my-snap-name": path "this/file/does/not" does not exist
+                2024/12/20 11:25:37.751693 container.go:411: in snap "my-snap-name": path "this/file/does" does not exist
+                error: something happened
+                2024/12/20 11:25:37.751697 container.go:411: in snap "my-snap-name": path "this/file" does not exist
+                2024/12/20 11:25:37.751700 container.go:411: in snap "my-snap-name": path "this" does not exist
+                error: referenced command not found in snap
+                """
+            ),
+        )
+    )
+
+    assert str(error) == "Snapd failed to pack"
+    assert error.details == "referenced command not found in snap"
+    assert error.resolution is None
+    assert error.docs_url is None
+
+
+def test_snap_pack_error_no_error_lines():
+    error = errors.SnapPackError(
+        call_error=subprocess.CalledProcessError(
+            returncode=1,
+            cmd=["snap", "pack"],
+            stderr=textwrap.dedent(
+                """\
+                2024/12/20 11:25:37.751687 container.go:411: in snap "my-snap-name": path "this/file/does/not" does not exist
+                2024/12/20 11:25:37.751693 container.go:411: in snap "my-snap-name": path "this/file/does" does not exist
+                2024/12/20 11:25:37.751697 container.go:411: in snap "my-snap-name": path "this/file" does not exist
+                2024/12/20 11:25:37.751700 container.go:411: in snap "my-snap-name": path "this" does not exist
+                """
+            ),
+        )
+    )
+
+    assert str(error) == "Snapd failed to pack"
+    assert error.details == "snapd did not report an error"
+    assert error.resolution is None
+    assert error.docs_url is None
+
+
+def test_snap_pack_error_no_stderr():
+    error = errors.SnapPackError(
+        call_error=subprocess.CalledProcessError(
+            returncode=1,
+            cmd=["snap", "pack"],
+        )
+    )
+
+    assert str(error) == "Snapd failed to pack"
+    assert error.details == "snapd did not report an error"
+    assert error.resolution is None
+    assert error.docs_url is None